DOVER — Feral swine have been expanding their range in the United States in the past few decades, and although their population remains small in New Hampshire, officials here are monitoring the trend.

Wild pigs are already well-established in southern states, California and Texas, where they’ve devastated crops and wildlife habitat with their voracious rooting and wallowing. There have been sporadic sightings in New Hampshire for more than a century, but the state only recently confirmed a significant population.

Mark Ellingwood, a Fish and Game wildlife biologist, estimates there are fewer than 500 feral hogs in the state, mostly in Grafton, Sullivan and Cheshire counties, but damage complaints and sightings are on the rise. In addition to property damage — the swine can dig two-foot-deep gouges with their snouts — the state is concerned that the boars will out-compete native wildlife for food given that they multiply rapidly and will consume nearly anything they come across, Ellingwood said.

The U.S. Department of Agriculture has been helping landowners who have had property damaged by wild boars through trapping and shooting, while state officials have tried to raise public awareness.

“We want people to be aware of the threats they pose to our natural environment, both plant communities and wildlife,” Ellingwood said.

Officials believe the state’s wild boar population originates from Corbin Park, a private, fenced-in shooting preserve that covers large parts of Croydon and several surrounding towns. The 24,000 acre preserve was founded in 1890 and is known for its extremely limited membership.

Scott Gilroy of the Blue Mountain Forest Association, which runs the park, said it would be impossible to estimate how many wild boar are in the park or have escaped from it over the years. He said he’s heard of half a dozen or so being killed by hunters outside the park each winter.

“Obviously several of them have gotten out because we’ve found places where the fences have been cut (by poachers). I think this would qualify very much as a nuisance rather than a plague,” he said.New Hampshire hunting regulations do not classify feral swine as wild game. Instead, the animals are considered escaped private property and may only be hunted with permission of the property owner. But because the boar population is linked to the game park, the park has given permission for licensed hunters to kill the animals outside the park.Feral swine populations in the northeast are relatively sparse, but there also are confirmed populations in New Jersey, New York and Pennsylvania.

In addition to common domesticated pigs, there are two main types of feral hogs in the United States. One was introduced by Spanish settlers, such as Christopher Columbus, who brought hogs into the territory around Florida.

Another variety, called the European wild boar or Russian hog, was introduced by European settlers for hunting purposes. Over the years, the pigs have naturally escaped or been set loose into the wild, yielding free-roaming boar populations.

European boars typically have larger shoulders and smaller hind legs than their Spanish counterparts, with long, dark brown hair. Hogs in the south are more varied in color and appearance.Parker Hall, state director of USDA’s Wildlife Services office in New Hampshire, said federal agencies are concerned about the growth of the wild pig populations, since the animals are an invasive species. They account for billions worth of lost revenue each year, whether it be through damage to crops or harm to other plants and animals.The particular concern pigs present in New Hampshire is the threat to livestock and other native species. Hall said there’s no reason to believe a pig population couldn’t thrive around New Hampshire’ Seacoast, given the opportunity. And that opportunity could be as simple as a pig getting loose from the back of a truck.

“They can get into some of the tidal areas and probably root and dig, and probably do very good on the Seacoast,” Hall said. “As I said, you’re only a truckload away...”